Refrigerant for providing ultra-low temperature

ABSTRACT

A mixed refrigerant comprising one member selected from R-23, R-116 and a mixture thereof and one member selected from propane, butane and a mixture thereof. The mixed refrigerant allows cooling the inside of a freezer to a super low temperature, particularly to a temperature of −60° C. or lower, with a compressor of a conventional freezer. The mixed refrigerant not only has a low boiling point similar to those of R-23 and R-116, but also can be liquefied in a room temperature surrounding due to propane or butane contained therein, and further has good miscibility with a lubricating oil or the like so that a freezer unit using the refrigerant is free from the problem of clogging therein. Additionally, the mixed refrigerant has no ability to deplete ozone and is significantly low with respect to greenhouse effect. The refrigerant can be liquefied by a pressure within the range of practical ability of a compressor in a room temperature surrounding and allows achieving with ease a temperature inside a freezer of −60° C. or lower by means of a freezer unit using one gas and one compressor.

TECHNICAL FIELD

The present invention relates to a working fluid used as a refrigerantin refrigerators and for other purposes. More particularly, the presentinvention relates to a refrigerant for providing an ultra-lowtemperature which does not possess any ozone destruction capability,thereby enabling to notably inhibit the influence thereof on theatmosphere of the earth (facilitating the reduction of the ‘green-house’effect), and which can be easily used at the same capacity as that of acompressor used in conventional refrigeration rooms or chambers.

BACKGROUND ART

Recently, refrigeration rooms at a ultra-low cooling temperature of lessthan −50° C. to −60° C., which is lower than conventional refrigerationrooms, have been used with development of the biotechnology and foodtransportation systems, and demand of such refrigeration rooms areincreasing.

In the field of biotechnology, cells, biological tissues and otherbiological substances have to be stably stored for an extended time ofperiod at the above-mentioned ultra-low temperature to ensure their goodsurvival activity rate after thawing. To satisfy this requirement, therefrigeration rooms used for cells and other biological substances needto have highly increased refrigerating power, along with a highreliability and a low maintenance cost. Further, in order to enablebiotechnology to be applied in hospitals and other institutions inaddition to application in laboratories, the refrigeration rooms have tobe constructed simply, at low cost; and also need to be easy to operate.

Similar problems also occur in food transportation systems etc. Tomaintain freshness of the food for a long period, the refrigerationrooms used in the transportation system must have high refrigeratingpower without any problems such as system failure, along with easymaintenance and low operation cost.

Under these circumstances, it is preferable to provide refrigerationrooms in which a refrigerant is repeatedly used in refrigeration cycles.However, refrigerants capable of providing an ultra-low coolingtemperature of less than −50° C. can not be easily liquefied at roomtemperature, because the critical pressure thereof is generallyincreased with the reduction of the standard boiling point, and have alow critical temperature.

Hitherto, a refrigerator unit, based on a multistage cooling cycle,using two or more refrigerants having different boiling points has beenused as a refrigerator for ultra-low temperature. Namely, by using arefrigerant having a high boiling point capable of being liquefied atroom temperature for a refrigeration process that liquefies arefrigerant having a lower boiling point, an ultra-low temperature canbe obtained.

A multistage cooling cycle-based refrigerator unit is illustrated in,for example, FIG. 1 in which two types of refrigerants are used and twosets of refrigerator units are operated with two compressors at twostages, respectively.

In the illustrated refrigerator room, a first refrigerant is compressedin a high temperature side-positioned compressor 1 and the gaseouscompressed refrigerant is subjected to heat radiation and cooling in ahigh temperature side-positioned condenser 3 provided with a fan 2,thereby producing a liquefied first refrigerant. The liquefied firstrefrigerant is guided through a capillary tube 5 to an outer tube 11 ofthe double tubed heat exchanger 10. After the vaporized firstrefrigerant in the outer tube 11 is used to cool a second refrigerant inan inner tube 12 of the heat exchanger 10, the first refrigerant isreturned to the high temperature side-positioned compressor 1. In theabove process, the reference numerals 6 and 7 represent a drier and aliquid separator (accumulator), respectively.

A second refrigerant, after being compressed in a low temperatureside-positioned compressor 20, is led into an inner tube 12 of the heatexchanger 10, and is cooled and liquefied with the first refrigerant.The liquefied second refrigerant is guided through a capillary tube 15to a low temperature side-positioned evaporator 30. In the evaporator30, the second refrigerant is vaporized under a reduced pressure tothereby cool the interior of the refrigerator room. The used secondrefrigerant is returned again to the compressor 20. In the aboveprocess, the reference numerals 26 and 27 represent a drier and an oilseparator for removing mist-like oil, respectively.

In the above illustrated refrigeration system, it becomes possible toprovide an ultra-low temperature which has a system power and capacitycomparable to conventional refrigeration rooms. However, because it isconstructed from two sets of refrigerators, the total size of therefrigeration system is increased and has a complicated structure,thereby causing difficulty in maintenance, substantially increasing thecost of the refrigeration room.

Alternatively, as illustrated in FIG. 2, a single compressor multicyclerefrigeration system in which a mixture of two or more refrigerantshaving different properties such as different boiling points is used incombination with a single compressor has been researched.

In the illustrated refrigeration system, three types of refrigerants arepreviously mixed to obtain a mixed refrigerant. The mixed refrigerant iscompressed in a compressor 40 provided with a fan 2, followed by beingsubjected to heat radiation in a condenser 41 to thereby liquefy a firstrefrigerant having the highest critical temperature.

The liquefied first refrigerant is then separated in a liquid separator45 to remove and recover therefrom an mist-like oil contaminated by thecompressor 40 and return the oil to the compressor 40. The separatedfirst refrigerant is vaporized in a heat exchanger 50 to simultaneouslycool and liquefy a gaseous second refrigerant having a lower criticaltemperature than that of the first refrigerant. The second refrigerantliquefied in the heat exchanger 50 is separated in a liquid separator 46and then vaporized in a heat exchanger 51 in which a third refrigeranthaving the lowest critical temperature is cooled and liquefied with thevaporized second refrigerant. The third refrigerant liquefied in theheat exchanger 51 is vaporized in an evaporator 55. The thus theproduced vapor of the third refrigerant is used to cool the interior ofthe refrigeration room to a predetermined ultra-low temperature.

In the above refrigeration system, the first to third refrigerantsvaporized in the heat exchangers 50 and 51 and the evaporator 55 arereturned through a common return pipe 61 to the compressor 40.

Using the illustrated refrigeration system, it becomes possible toreduce the amount of machinery utilized in the refrigeration roombecause only one compressor is included therein. However, contrary tothis advantage, the flow circuit for circulating the three refrigerantsis complicated and thus the total size of the refrigeration room isunavoidably increased along increased difficulty of the maintenance.

In addition to the improvement of the refrigeration system, animprovement of the refrigerant used as the working liquid therein hasbeen also made. Hitherto, fluorohydrocarbons which are generallyreferred to as “flons” have been used as refrigerants. However, due torecent evidence proving that flon gas can cause destruction of the ozonelayer adding to global warming, such flons are prohibited from beingused as refrigerants. Namely, use of “specified flons” capable ofcausing notable ozone destruction and flons capable of addingsubstantially to general global warming can not be used underestablished regulations. Therefore, it is highly desirable to develop anovel refrigerant which has zero ozone destruction properties and anegligible effect on global warming.

At present, many types of the refrigerants which can be used withoutcausing any adverse effect on the environment and which can showexcellent properties comparable to those of the conventional flons havebeen proposed as an alternative to the above-described specified flonsand other flons.

For example, a two component or three component refrigerant includingperfluoroethane, ethane and trifluoromethane along with 1 to 10% byweight of propane and butane having a good affinity with lubricating oilhas been disclosed in Japanese Unexamined Patent Publication (Kokai) No.5-186765. This reference discloses that the return of the lubricatingoil to the compressor can be accelerated with use of propane and butane,however, the cooling temperature and the pressure applied during theliquefication process is not taught.

Further, a mixed refrigerant including trifluoromethane and ethane orhexafluoromethane and ethane, and having a reduced standard boilingpoint of −90° C. or less has been disclosed in Japanese UnexaminedPatent Publication (Kokai) No. 7-48563. However, due to a low criticaltemperature and a high critical pressure, the mixed refrigerant can notbe used in conventionally single cycle refrigeration rooms.

Furthermore, the applicant of this application has suggested arefrigerant having an ozone destruction capability of zero level whichinhibits global warming in Japanese Unexamined Patent Publication(Kokai) Nos. 5-306391 and 7-48562. JPP'391 teaches the use of arefrigerant mixture of dihydrotetrafluoroehane (CH²-FCF³; generallyreferred to as “HFC-134a” or “R-134a”) and trifluoromethane (CHF₃;generally referred to as “HFC-23” or “R-23”), and JPP'562 teaches use ofa refrigerant mixture of dihydrotetrafluoroehane (R-134a) andperfluoroethane (C₂F₆; generally referred to as “FC-116” or “R-116”).

When additives such as propane, butane or other hydrocarbons are addedto refrigerants described in JPP'391 and '562, it becomes possible toreduce the internal temperature of the refrigeration room to less than−50° C. at a discharge pressure of about 20 Kg/cm², which can be appliedeffectively to conventional single cycle refrigeration rooms. Therefore,the above-mentioned refrigerants can be advantageously used inrefrigerators and other devices; however, to satisfy the above-describedrequirements for refrigeration in the field of biotechnology, foodtransportation systems etc., it is more desirable to provide an improvedrefrigerant capable of ensuring a remarkably reduced temperature of therefrigeration room which is significantly lower than −50° C.

In view of the above-described problems of the prior art refrigerants,one object of the present invention is to provide a working fluid whichcan ensure an ozone destruction capability of zero level and inhibitedglobal warming properties which can achieve a satisfactory ultra-lowtemperature by means of conventional compressors. Particularly, thepresent invention is directed to provide a refrigerant which can easilyrealize a refrigeration ambient temperature of less than −60° C., whenthe refrigerant is used in the conventional single cycle refrigerationrooms.

DISCLOSURE OF INVENTION

In order to achieve the above mentioned object, there is provided arefrigerant for providing an ultra-low temperature in which therefrigerant includes trifluoromethane (CHF3), perfluoroethane (C₂F₆),and a conventional fuel selected from the following fuels: propane,butane, or a mixture of propane and butane.

Preferably, the trifluoromethane and the perfluoroethane are containedin a mixing ratio of 70% to 15% by weight of trifluoromethane, and 30%to 85% by weight of perfluoroethane.

Preferably, the propane is included by an amount 55% to 95% by weight,the butane is included by an amount 50% to 90% by weight, or the mixtureof propane and butane is included by an amount 35% to 70% by weight.

According to another aspect of the present invention, there is provideda refrigerant for providing an ultra-low temperature, in which therefrigerant comprises trifluoromethane (CHF₃), propane and butane.

Preferably, the refrigerant comprises 60% to 15% by weight oftrifluoromethane, 16% to 34% by weight of propane and 24% to 51% byweight of butane.

According to another aspect of the present invention, there is provideda refrigerant for providing an ultra-low temperature, in which therefrigerant comprises trifluoromethane (CHF₃) and butane.

Preferably, the refrigerant comprises 50% to 15% by weight oftrifluoromethane and 50% to 85% by weight of butane.

According to another aspect of the-present invention, there is provideda refrigerant for providing an ultra-low temperature, in which therefrigerant comprises perfluoroethane (C₂F₆), propane and butane.

Preferably, the refrigerant comprises 60% to 20% by weight ofperfluoroethane, 16% to 32% by weight of propane, and 24% to 48% byweight of butane.

According to another aspect of the present invention, there is provideda refrigerant for providing an ultra-low temperature, in which therefrigerant comprises perfluoroethane (C₂F₆) and butane.

Preferably, the refrigerant comprises 55% to 20% by weight ofperfluoroethane and 45% to 80% by weight of butane.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will be more clearly understood from thedescription as set forth below with reference to the accompanyingdrawings, wherein:

FIG. 1 is a refrigeration room of the prior art using two types ofrefrigerants and two sets of refrigerator units;

FIG. 2 is a refrigeration room of the prior art, based on a singlecompressor-multicycle system using three types of the mixedrefrigerants;

FIG. 3 is a graph showing the effect of addition of propane and butaneto a gas mixture of R-23 and R-116;

FIG. 4 is a graph showing the effect of addition of propane and butaneto a gas mixture of R-23 and R-116 having different mixing ratios;

FIG. 5 is a graph showing the effect obtained upon the sole addition ofpropane to a gas mixture of R-23 and R-116,

FIG. 6 is a graph showing the effect obtained upon the sole addition ofbutane to a gas mixture of R-23 and R-116,

FIG. 7 is a graph showing the effect obtained upon addition of propaneand butane to a refrigerant consisting of R-23;

FIG. 8 is a graph showing the effect obtained upon addition of propaneand butane to a refrigerant consisting of R-116;

FIG. 9 is a graph showing the effect obtained upon sole addition ofbutane to a refrigerant consisting of R-23; and

FIG. 10 is a graph showing the effect obtained upon sole addition ofbutane to a refrigerant consisting of R-116.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be further described with reference to thepreferred embodiments of the present invention.

In the process of seeking a novel generation of refrigerants which showzero ozone destruction properties and prevents global warming and whichcan be used as an alternative to conventional chlorine-containingrefrigerants or bromine-containing refrigerants such as flons andhalons, the inventors of this application have found that if arefrigerant is prepared by combining a specific hydrocarbon(s) to a gasmixture consisting of trifluoromethane (CHF₃; R-23) and perfluoroethane(C₂F₆; R-116), or a sole gas of R-23 or R-116, the resulting refrigerantcan maintain its boiling point at a low temperature, and the refrigerantcan be liquefied at a temperature and pressure within a range of actualuse.

Due to absence of chlorine atom(s) in a molecule thereof, both of R-23and R-116 can exhibit only a negligible global warming. A gas mixture ofR-23 and R-116, as is shown in the example concerning the mixing ratioof R-23 and R-116 of 39/61 in the following Table 1, can exhibit aboiling point of around −80° C., namely, it can achieve a markedlyreduced temperature (i.e., ultra-low temperature). However, since it cansimultaneously exhibit a notably increased vapor pressure of around 40atm at room temperature, the gas mixture can not be applied to theconventional refrigeration rooms because of insufficient power of theinstalled compressor.

However, as a result of in-depth study, the inventors have surprisinglyfound that the gas mixture can retain its low boiling point and thus itcan be liquefied at a pressure of around 20 atm at room temperature, ifpropane, butane or a mixture thereof is added to the gas mixture.

Propane and butane are gases which are widely used as a fuel in dailylife, and thus they can be easily handled without a high level of skill.As is apparent from the properties of propane and butane summarized inthe following Table 2, these gases can show a low vapor pressure at roomtemperature, but exhibit a high standard boiling point, and thus theycan not be solely used as a refrigerant for an ultra-low temperature.However, the inventors have found that the above properties of propaneand butane can be similarly realized only when they are added solely oras a gas mixture of R-23 and R-116. The inventors have also confirmedfrom experimentation that all the resulting refrigerants can satisfy therequirements for the properties necessary for ultra-low temperaturerefrigerants.

TABLE 1 Boiling Critical Vapor Chemical Point Temp. Pressure Componentformula (° C., latm) (° C.) (atm, 20° C.) R-23 CHF₃ −82.2 26.15 49.3R-116 CF₃ CF₃ −78.2 19.85 30.4 Mixture R-23/R-116 = −85.7 — 41.2 of R-23& 39/61 R-116

TABLE 2 Boiling Critical Vapor Hydro- Chemical Point Temp. PressureCarbons Formula (° C., latm) (° C.) (atm, 20° C.) Propane C₃H₈ −42.1152.0 8.4 Butane C₄H₁₀ −0.5 153.2 2.1

Generally speaking, properties such as the boiling point of the gasmixture can be represented by a continuous curve obtained by plotting aboiling point or other properties of each component constituting the gasmixture and thus the gas mixture can exhibit an intermediate property ofall the constituent components. However, contrary to this, according tothe inventors' findings, when specific alternative fluorocarbons, i.e.,the above-described R-23, R-116 or a mixture thereof., are mixed withpropane, butane or a mixture thereof to obtain a gas mixture having apredetermined composition, the resulting gas mixture can maintain a lowboiling point which is inherent in R-23, R-116 or a mixture thereof, andat the same time, it can exhibit a low vapor pressure which is inherentin both propane and butane. Accordingly, as described above, therefrigerant of the present invention can ensure the specific area of theproperties which are suitable for the ultra-low temperature refrigerant.

At the present stage, the reason why the described gas mixture of thepresent invention can strongly generate the specific property, and exactmechanism of each of the constitutional components are not yetclarified. However, it should be noted that the properties of the gasmixture having the predetermined composition obtained upon addition ofpropane and/or butane to R-23, R-116 or a mixture thereof can bereliably achieved, and are stable.

Accordingly, the refrigerant of the present invention formed from theabove-described components can be used in any conventional refrigerationroom, and can easily achieve an ultra-low temperature in suchrefrigeration rooms. Accordingly, no specific modification to therefrigeration rooms is required.

The refrigerant of the present invention will be further described withreference to the following experimental data.

The relationship between the compositions in which the components R-23,R-116, propane and butane are contained in different mixing ratios, andthe properties as the refrigerant was evaluated in accordance with thefollowing experiments (1) to (8) was conformed. Note that in experiments(1) to (4), the refrigerants having different compositions were preparedby combining a gas mixture of R-23 and R-116 with propane, butane or amixture thereof. In experiments (5) to (8), the refrigerants havingdifferent compositions were prepared by combining a sole gas of R-23 orR-116 with propane, butane or a mixture thereof.

(1) Effects Obtained upon Addition of Propane and Butane to a GasMixture of R-23 and R-116

The refrigerants of the present invention were prepared by using a gasmixture of R-23 and R-116 (mixing ratio=39:61). Different amounts ofpropane and butane were added to the gas mixture as is shown in thefollowing Table 3 to obtain refrigerants having different compositions.

Each refrigerant was charged in the refrigeration room (refrigeratingcompressor commercially available from Damphos & Co.), and thecompressor was operated in accordance with the conventional mannerdescribed in the operation manual to determine a temperature inside therefrigeration room (hereinafter, briefly referred to as “ambienttemperature”, ° C.), and a discharge pressure (kgf/cm², gauge pressure)and suction pressure (kgf/cm², absolute pressure) of the compressor. Theresults are summarized in the following Table 3.

TABLE 3 C₃H₈ + C₄H₁₀ Ambient Discharge Suction No. (wt %) Temp. (° C.)Pressure Pressure 1 100 −41 3.8 0.421 2 93.3 −41 5.3 0.557 3 87.5 −427.8 0.625 4 82.4 −45 10.0 0.829 5 77.8 −50 12.0 0.897 6 73.7 −52 14.01.033 7 70.0 −58 16.0 1.133 8 68.9 −68 20.0 1.383 9 63.3 −73 18.8 1.58310 60.8 −75 20.0 1.433 11 59.6 −74 17.8 1.433 12 54.4 −75 19.0 1.383 1340.0(B) −33 25.0 1.533 14 38.9(A) −73 19.5 1.733 15 37.8(A) −71 20.01.833 16 36.8(A) −71 21.0 1.833 17 35.9(A) −66 24.1 2.233 18 30.0(B) −2726.0 1.733 19 20.0(B) −17 28.0 1.833 20 10.0(B) −12 30.0 2.033 21 0.0−85.7 41.2 — (b.p.) (vapor press.) Note: Room Temperature: 20° C.Discharge Pressure: Gauge Pressure (kgf/cm²) Vacuum: Absolute Pressure(kgf/cm²) R-23/R-116 = 39/61 C₃H₈/C₄H₁₀ = 25/75 except for Nos. 2 to 7:C₃H₈/C₄H₁₀ = 15.5/139.5 − 140/15 Total of Charged Gases: 150 to 285 gexcept for (A): 360 to 390 g, (B): 210 g (constant)

In Table 3, for reference, the ambient temperature and dischargepressure of the refrigerant No.21 containing no propane and butane (0 wt%) are described with reference to the boiling point and the vaporpressure at the room temperature of the gas mixture of R-23 (39 wt %)and R-116 (61 wt %), respectively. The results of Table 3 are alsoplotted in FIG. 3.

As can be appreciated from FIG. 3, when a mixture of propane and butanewere mixed in a mixing ratio of 35 to 70% by weight to a gas mixture ofR-23 and R-116, the ambient temperature could be maintained at a rangeof −60 to −75° C., and the refrigerating compressor could be operated ata discharge pressure of around 15 to 25 kgf/cm² at an outlet of thecompressor.

Further, when a mixing ratio of propane/butane mixture was changed to arange of 35% to 65% by weight, an ambient temperature of less than −70°C. could be achieved at a relatively low discharge pressure of 18 to 22kgf/cm².

Furthermore, the refrigerants satisfying the above-mentionedrequirements of the composition have good compatibility with lubricatingoil and therefore they do not cause any problems due to clogging, whenthe above experiments are repeated.

When a mixing ratio of propane/butane mixture to the gas mixture isincreased beyond an upper limit of the described composition range asindicated in FIG. 3, the ambient temperature is suddenly increased toend at around −41° C., while the discharge pressure is graduallyreduced. Conversely, when a mixing ratio of propane/butane mixture tothe gas mixture is reduced, the refrigeration process becomes sensitiveto the amount and composition of the charged gases at a mixing ratio ofaround 40% by weight, and therefore notable differences in the coolingpower can be produced along with an increase of pressure, depending uponthese operation conditions.

FIG. 3 includes the results classified under Group (A) and Group (B).

The Group (A) shows the results obtained at a total amount of chargedgases of 360 g to 390 g when the ambient temperature is maintained atthe temperature as low as possible. Even if the mixing ratio is reducedto 40% by weight or less, the ambient temperature can be maintained atthe substantially same temperature of about −70° C. However, when themixing ratio is further reduced to about 35% by weight, overcharging ofthe gases is caused, thus both of the discharge pressure and the ambienttemperature are increased to the level which does not ensure asufficient cooling power.

When the refrigerating compressor was operated at a total amount ofcharged gases of 210 g (constant), shown as Group (B) in FIG. 3, themixing ratio of 40% by weight or less resulted in an ambient temperatureof greater than −40° C., i.e., remarkably reduced cooling power. Thisresult indicates that the liquefication of R-23 and R-116 can not beproceeded under operation conditions including the described totalamount of charged gases.

(2) Effects Obtained upon Addition of Propane and Butane to a GasMixture of R-23 and R-116 Having Different Mixing Ratios

The procedure of the above experiment (1) was repeated to confirm thatthe refrigerant can achieve excellent properties described above, withina wide range of the mixing ratios of R-23 and R-116, a mixing ratio ofpropane and butane was adjusted to a predetermined ratio of 25:75, but amixing ratio of R-23 and R-116 was varied as shown in the followingTable 4. The results are summarized in the following Table 4.

TABLE 4 R-116 Ambient Discharge Suction No. (wt %) Temp. (° C.) PressurePressure 1 30 −59 27.0 0.877 2 40 −64 26.4 0.884 3 50 −73 23.4 1.733 470 −70 23.0 1.583 5 80 −68 21.8 1.483 6 90 −55 21.0 1.483 Note: RoomTemperature: 20° C. Discharge Pressure: Gauge Pressure (kgf/cm²) Vacuum:Absolute Pressure (kgf/cm²) R-116 (wt %): R-116/(R-23 + R-116) × 100 (wt%) C₃H₈/C₄H₁₀ = 25/75 (constant) (R-23 + R-116)/(C₃H₈ + C₄ ₁₀) = 50/50Total of Charged Gases: 210 g

The results of Table 4 are also plotted in FIG. 4. As can be appreciatedfrom FIG. 4, an ambient temperature of about −60 to −73° C. can bemaintained and also the compressor can be operated at a dischargepressure of not more than 26 kgf/cm², when a mixing ratio of R-116 inR-23 and R-116 is in the range of about 30 to 85 wt % (70 to 15 wt % forR-23), and in particular, a mixing ratio of R-23 and R-116 is around 50%by weight.

When the mixing ratio of R-23 and R-116 is increased above or reducedbelow the range of the mixing ratio, the ambient temperature can beincreased in both of the R-23-rich area and R-116-rich area, and thedischarge pressure shows a tendency of being increased at the area ofthe R-116 content of less than 50% by weight.

The above results indicate that according to the present invention,excellent functions and effects can be obtained in a relatively widerange of the mixing ratio of R-23 and R-116, and the ambient temperatureof −60 to −70° C. can be achieved when R-116 is used in the abovementioned range of mixing ratio, however, if it is desired to maintainthe discharge pressure at a low level, R-116 is preferably used in amixing ratio of more than 50%.

In particular, when R-116 is used in a mixing ratio of 45% to 65% byweight, an ambient temperature of less than −70° C. can be retained atthe discharge pressure of 23 kgf/cm².

(3) Effects Obtained upon Sole Addition of Propane to a Gas Mixture ofR-23 and R-116

The procedure of the above experiment (1) was repeated, to confirm theeffects obtained when the refrigerant of the present invention isprepared by mixing a gas mixture of R-23 and R-116 with propane alone, amixing ratio of R-23 and R-116 was adjusted to a predetermined ratio of39:61. However, a mixing ratio of propane to the gas mixture of R-23 andR-116 was varied as shown in the following Table 5. The results aresummarized in the following Table 5.

TABLE 5 Propane Ambient Discharge Suction No. (wt %) Temp. (° C.)Pressure Pressure 1 10 −2 30.0 0.897 2 50 −51 24.8 1.633 3 80 −67 14.41.233 4 90 −65 14.0 1.233 Note: Room Temperature: 20° C. Dischargepressure: gauge pressure (kgf/cm²) Vacuum: absolute pressure (kgf/cm²)R-23/R-116 = 39/61 (constant) Total of charged gases: 210 g

The results of Table 5 are also plotted in FIG. 5. In FIG. 5, forreference, the ambient temperature and discharge pressure of therefrigerants containing no (0 wt %) propane and containing 100% byweight of propane are plotted with reference to the boiling point andthe vapor pressure at room temperature of the gas mixture of R-23 (39 wt%) and R-116 (61 wt %), and propane alone, respectively.

As can be appreciated from FIG. 5, the ambient temperature is suddenlyreduced immediately after a mixing ratio of propane to the gas mixtureof R-23 and R-116 is reduced at the area near to the propane content of90% by weight, while a discharge pressure is retained at a relativelylow level. Further, when the mixing ratio of propane is reduced to 50%by weight or less, the operation of the refrigerator unit becomesinstable so that a constant ambient temperature can not be obtained.

The above results indicate that the refrigerator can be operated at aconstantly maintained ambient temperature of about −60 to −67° C. andwith a discharge pressure of about 13 to 22 kgf/cm², if propane is mixedin a mixing ratio of 55 to 95% by weight to a gas mixture of R-23 andR-116.

In particular, the above refrigerant is suitable as a refrigerantcapable of achieving an ambient temperature of less than −65° C. underthe operation conditions of the propane mixing ratio of 65% to 85% byweight and the discharge pressure of not more than 20 kgf/cm².

(4) Effects Obtained upon Sole Addition of Butane to a Gas Mixture ofR-23 and R-116

The procedure of the above experiment (1) was repeated to confirm theeffects obtained when the refrigerant of the present invention isprepared by mixing a gas mixture of R-23 and R-116 with butane alone. Amixing ratio of R-23 and R-116 was adjusted to a predetermined ratio of39:61. However, a mixing ratio of butane to the gas mixture of R-23 andR-116 was varied as is shown in the following Table 6. The results aresummarized in the following Table 6.

TABLE 6 Butane Ambient Discharge Suction No. (wt %) Temp. (° C.)Pressure Pressure 1 50 −29 19.0 1.333 2 80 −38 9.5 0.625 3 90 −32 6.00.557 Note: Room Temperature: 20° C. Discharge Pressure: Gauge Pressure(kgf/cm²) Vacuum: Absolute Pressure (kgf/cm²) R-23/R-116 = 39/61(constant) Total of Charged Gases: 210 g

The results of Table 6 are also plotted in FIG. 6. In FIG. 6, forreference, the ambient temperature and discharge pressure of therefrigerants containing no (0 wt %) butane and containing 100% by weightof butane are plotted with reference to the boiling point and the vaporpressure at the room temperature of the gas mixture of R-23 (39 wt %)and R-116 (61 wt %), and butane alone, respectively.

As can be appreciated from FIG. 6, the ambient temperature is suddenlyreduced immediately after a mixing ratio of butane to the gas mixture ofR-23 and R-116 is reduced at the area near to the butane content of 90%by weight, while an increase of the discharge pressure is moderate andthus the pressure is retained at a relatively low level. Namely, theabove tendency is similar to that of experiment (3) using propane alone.Further, when the mixing ratio of butane is reduced to 50% by weight orless, the operation of the refrigerator unit becomes instable so that aconstant ambient temperature can not be obtained.

In addition, it is also appreciated from FIG. 6 that the ambienttemperature of −30° C. to −40° C. can be obtained when a mixing ratio ofbutane is in the range of 50% to 90% by weight, and at the same time, alow discharge pressure of 6.0 to 19 kgf/cm² can be obtained. It istherefore considered that the refrigerant having the above compositioncan be advantageously used for refrigerators which do not requirenotably reduced refrigeration temperature, as refrigerators using thisrefrigerant can be operated with a small load.

Also, the above refrigerant is suitable as a refrigerant capable ofachieving an ambient temperature of not higher than −35° C. under thedischarge pressure of less than 15 kgf/cm² in the butane mixing ratio of60 to 80% by weight.

(5) Effects Obtained upon Addition of Propane and Butane to aRefrigerant Consisting of R-23

To confirm the properties of the refrigerant according to the presentinvention consisting of R-23 and a mixture of propane and butane, R-23was mixed with a mixture of propane and butane (mixing ratio =40:60).Different amounts of propane and butane were added to R-23 as shown inthe following Table 7 to obtain the refrigerants having differentcompositions.

Each refrigerant was charged in the refrigeration room (refrigeratingcompressor commercially available from Damphos & Co.), and thecompressor was operated in accordance with the conventional mannerdescribed in the operation manual to determine an ambient temperature (°C.), and a discharge pressure (kgf/cm², gauge pressure) and vacuum(kgf/cm², absolute pressure) of the compressor. The results aresummarized in the following Table 7.

TABLE 7 C₃H₈ + C₄H₁₀ Ambient Discharge Suction No. (wt %) Temp. (° C.)Pressure Pressure 1 82.4 −60 17.0 0.000 2 81.3 −63 19.5 0.001 3 80.0 −6322.0 0.001 4 78.6 −61 23.0 0.003 5 77.8 −75 17.5 0.001 6 76.5 −70 21.80.004 7 65.0 −72 19.0 0.003 8 61.9 −72 18.5 0.003 9 59.1 −72 19.5 0.00310 40.0 −65 23.0 0.003 Note: Room Temperature: 28° C. DischargePressure: Gauge Pressure (kgf/cm²) Vacuum: Absolute Pressure (kgf/cm²)C₃H₈/C₄H₁₀ = 40/60 Total of Charged Gases: 140 to 220 g

The results of Table 7 are also plotted in FIG. 7. In FIG. 7, for thereference, the ambient temperature and discharge pressure of therefrigerant containing no (0 wt %) mixture of propane and butane areplotted with reference to the boiling point and the vapor pressure atthe room temperature of R-23.

As can be appreciated from FIG. 7, when a mixture of propane and butanewere mixed in a mixing ratio of 40 to 85% by weight (16 to 34% by weightof propane and 24 to 51% by weight of butane) to R-23, a mixing ratio ofR-23 being in a range of 60 to 15% by weight, the ambient temperaturecould be maintained at −60° C. or less, and the refrigerating compressorcould be operated at a discharge pressure of around 17.0 to 23.0 kgf/cm²in an outlet of the compressor.

(6) Effects Obtained upon Addition of Propane and Butane to aRefrigerant Consisting of R-116

The procedure of the above experiment (5) was repeated to confirm theproperties of the refrigerant consisting of R-116 and a mixture ofpropane and butane; R-116 was mixed with a mixture of propane and butane(mixing ratio=40:60). Different amounts of propane and butane were addedto R-116 as shown in the following Table 8 to obtain the refrigerantshaving different compositions. The results are summarized in thefollowing Table 8.

TABLE 8 C₃H₈ + C₄H₁₀ Ambient Discharge Suction No. (wt %) Temp. (° C.)Pressure Pressure 1 88.2 −52 8.5 0.340 2 83.3 −58 10.0 0.272 3 78.9 −6612.0 0.204 4 75.0 −68 13.0 0.000 5 73.7 −63 14.0 0.068 6 70.0 −65 15.00.000 7 68.4 −66 14.8 0.068 8 65.0 −68 15.0 0.000 9 63.2 −58 18.4 0.06810 61.1 −63 18.2 0.000 11 57.9 −65 19.2 0.001 12 55.0 −67 19.5 0.001 1352.4 −69 19.0 0.001 14 50.0 −69 18.0 0.001 15 47.8 −68 20.0 0.001 1640.0 −65 25.0 0.001 Note: Room Temperature: Gauge Pressure (kgf/cm²)vacuum: absolute pressure (kgf/cm²) C₃H₈/C₄H₁₀ = 40/60

Total of Charged Gases: 190 to 250 g

The results of Table 8 are also plotted in FIG. 8. In FIG. 8, forreference, the ambient temperature and discharge pressure of therefrigerant containing no (0 wt %) mixture of propane and butane areplotted with reference to the boiling point and the vapor pressure atthe room temperature of R-116.

As can be appreciated from FIG. 8, when a mixture of propane and butanewere mixed in a mixing ratio of 40 to 80% by weight (16 to 32% by weightof propane and 24 to 48% by weight of butane) to R-116, a mixing ratioof R-116 being in a range of 60 to 20% by weight, the ambienttemperature could be maintained at −60° C. or less, and therefrigerating compressor could be operated at a discharge pressure of12.0 to 25.0 kgf/cm² in an outlet of the compressor.

(7) Effects Obtained upon Addition of Butane to a Refrigerant Consistingof R-23

The procedure of the above experiment (5) was repeated to confirm theproperties of the refrigerant consisting of R-23 and butane, R-23 wasmixed with different amounts of butane, shown in the following Table 9,to obtain the refrigerants having different compositions. The resultsare summarized in the following Table 9.

TABLE 9 Butane Ambient Discharge Suction No. (wt %) Temp. (° C.)Pressure Pressure 1 88.9 −51 13.5 0.068 2 83.3 −69 18.6 0.002 3 78.9 −7220.0 0.003 4 75.0 −74 19.0 0.001 5 71.4 −75 17.9 0.001 6 65.1 −74 17.20.001 7 60.0 −74 21.0 0.004 8 50.0 −60 22.5 0.003 Note: RoomTemperatute: 28° C. Discharge Pressure: Gauge Pressure (kgf/cm²) Vacuum:Absolute Pressure (kgf/cm²) Total of Charged Gases: 190 to 230 g

The results of Table 9 are also plotted in FIG. 9. In FIG. 9, forreference, the ambient temperature and discharge pressure of therefrigerant containing no (0 wt %) butane are plotted with reference tothe boiling point and the vapor pressure at the room temperature ofR-23.

As can be appreciated from FIG. 9, when butane was mixed in a mixingratio of 50 to 85% by weight and thus R-23 was mixed in a mixing ratioof 50 to 15% by weight, the ambient temperature could be maintained at−60° C. or less, and the refrigerating compressor could be operated at adischarge pressure of 17.2 to 21.0 kgf/cm² in an outlet of thecompressor.

(8) Effects Obtained upon Addition of Butane to a Refrigerant Consistingof R-116

The procedure of the above experiment (5) was repeated to confirm theproperties of the refrigerant according to the present inventionconsisting of R-116 and butane, R-116 was mixed with different amountsof butane, shown in the following Table 10, to obtain the refrigerantshaving different compositions. The results are summarized in thefollowing Table 10.

TABLE 10 Butane Ambient Discharge Suction No. (wt %) Temp. (° C.)Pressure Pressure 1 80.0 −60 12.5 0.272 2 73.7 −63 12.8 0.204 3 72.7 −6315.0 0.000 4 71.4 −65 15.0 0.136 5 70.0 −69 15.0 0.068 6 68.4 −60 16.00.204 7 66.7 −72 15.3 0.027 8 65.2 −76 15.5 0.041 9 63.6 −68 15.8 0.00010 62.5 −73 15.7 0.027 11 61.9 −74 17.2 0.068 12 60.0 −71 15.7 0.000 1357.9 −70 17.2 0.068 14 56.5 −74 18.0 0.068 15 55.0 −71 17.0 0.068 1652.4 −69 18.0 0.000 17 50.0 −69 21.0 0.000 18 45.0 −60 22.5 0.000 Note:Room Temperature: 28° C. Discharge Pressure: Gauge Pressure (kgf/cm²)Vacuum: Absolute Pressure (kgf/cm²) Total of Charged Gases: 200 to 240 g

The results of Table 10 are also plotted in FIG. 10. In FIG. 10, forreference, the ambient temperature and discharge pressure of therefrigerant containing no (0 wt %) butane are plotted with reference tothe boiling point and the vapor pressure at the room temperature ofR-116.

As is appreciated from FIG. 10, when butane was mixed in a mixing ratioof 45% to 80% by weight and thus R-116 was mixed in a mixing ratio of55% to 20% by weight, the ambient temperature could be maintained at−60° C. or less, and the refrigerating compressor could be operated at adischarge pressure of 12.5 to 21.0 kgf/cm² at an outlet of thecompressor.

Industrial Applicability

As can be understood from the above detailed description, therefrigerant shows an ozone destruction capability of zero level and aninhibited warming-up effect of the earth, and therefore it can beutilized as alternative frons without causing any adverse effects on theenvironmental conditions.

Further, the refrigerant can be produced from R-23 and R-116 as well aspropane and butane gases which are conventional fuels, at a lowproduction cost. Also, the refrigerant can be easily and safely handled.

Furthermore, since the refrigerant material has specific properties, therefrigerant can be applied to conventional refrigeration rooms withoutmodifying the construction of the room and without requiring a newrefrigeration room to be installed therein such as a complicatedhigh-power refrigerator unit especially designed for the presentrefrigerant. Furthermore, in such conventional refrigeration rooms, therefrigerant can attain an ultra-low temperature, in particular, anambient temperature of less than −60° C. Moreover, refrigeration roomswhich can be used in practice are available at very low cost because oftheir simple construction, and also can be easily maintained. It istherefore expected that the refrigerant can largely contribute on a widevariety of industries including food transportation industrybiotechnology industry which has prospects of further development infuture.

What we claim is:
 1. A refrigerant for providing an ultra-lowtemperature, wherein said refrigerant comprises trifluoromethane (CHF₃),perfluoroethane (C₂F₆), and at least one or more members selected frompropane and butane, wherein said trifluoromethane and saidperfluoroethane are contained in a mixing ratio of 70% to 15% by weightof trifluoromethane, and 30% to 85% by weight of perfluoroethane, andsaid propane is included by an amount 55% to 95% by weight, said butaneis included by an amount 50% to 90% by weight, or said mixture ofpropane and butane is included by an amount 35% to 70% by weight.
 2. Arefrigerant for providing an ultra-low temperature, wherein saidrefrigerant comprises trifluoromethane (CHF₃), perfluoroethane (C₂F₆),and at least one or more members selected from propane and butane,wherein said propane is included by an amount 55% to 95% by weight, saidbutane is included by an amount 50% to 90% by weight, or said mixture ofpropane and butane is included by an amount 35% to 70% by weight.
 3. Arefrigerant for providing an ultra-low temperature, in which saidrefrigerant comprises trifluoromethane (CHF₃), propane and butane,wherein said refrigerant comprises 60% to 15% by weight oftrifluoromethane, 16% to 34% by weight of propane and 24% to 51% byweight of butane.
 4. A refrigerant for providing an ultra-lowtemperature, in which said refrigerant comprises trifluoromethane (CHF₃)and butane, wherein said trifluoromethane (CHF₃) and butane arecontained in a mixing ratio of 50% to 15% by weight of trifluoromethaneand 50% to 85% by weight of butane.
 5. A refrigerant for providing anultra-low temperature, in which said refrigerant comprisesperfluoroethane (C₂F₆), propane and butane, wherein said perfluoroethane(C₂F₆), propane and butane are contained in a mixing ratio of 60% to 20%by weight of perfluoroethane, 16% to 32% by weight of propane, and 24%to 48% by weight of butane.
 6. A refrigerant for providing an ultra-lowtemperature, in which said refrigerant comprises perfluoroethane (C₂F₆)and butane.
 7. The refrigerant according to claim 6, in which saidrefrigerant comprises 55% to 20% by weight of perfluoroethane and 45% to80% by weight of butane.